1. Field of the Invention
The present invention is directed to a dual band antenna and, in particular, to an H-field shielded loop antenna (for example, as used in radio frequency identification (RFID), passive telemetry and transcutaneous energy transfer) combined with an E-field antenna such as a wireless application antenna.
2. Description of Related Art
Electromagnetic interference (EMI) degrades optimum performance of electronic devices. Ideally, electronic devices should function in a state of electromagnetic compatibility (EMC) causing substantially no interference to and receiving substantially no interference from other electronic sources. In order to be compliant with EMC standards electronic devices are shielded to increase immunity to external perturbation and minimize unintentional radiation of the device.
Shielded loop antennas are currently used, for example, as an electromagnetic H-field inductor or receiving coil for radio frequency identification (RFID), passive telemetry and transcutaneous energy transfer, e.g., communication with implantable medical devices. The loop antenna comprises a shielded transmission line, e.g., coaxial line, stripline or microstrip line. However, often devices employ multiple antennas such as an H-field antenna and an E-field antenna used, for example, to communicate wirelessly with a remote control device. Shielding of an E-field wireless application antenna, i.e., an antenna that communicates with a wireless device such as an external control unit, personal computer, Personal Digital Assistant (PDA) or mobile/cellular phone, is impractical since substantially all radiation of signals necessary for wireless communication would be inhibited by the shield. Accordingly, heretofore when employing an H-field shielded loop antenna a second separate E-field wireless application antenna must be disposed outside or exteriorly of the shield. In this conventional configuration the use of two separate antenna devices undesirably increases the overall cost and size of the system.
It is therefore desirable to develop an integrated H-field shielded loop antenna and an E-field antenna while solving the aforementioned problems associated with conventional devices.